Turbochargers are utilized in engines for improving the output power of the engine by increasing the airflow charge to the cylinders to support an increased fuel charge. Turbochargers are well known devices for pressurizing intake air entering the combustion chambers of an internal combustion engine to thereby increase the efficiency and power output of the engine. In general, pressurizing the intake air increases the quantity of air entering the engine cylinders during the intake stroke, and this allows more fuel to be utilized in establishing a desired air-to-fuel ratio. Increased available engine output torque and power is thereby realized.
In a turbocharged engine, the exhaust manifold of the engine is fluidly coupled to a turbine component of the turbocharger via an exhaust conduit, and the exhaust gas flowing through the exhaust conduit causes a turbine wheel within the turbine to rotate at a rate determined by the pressure and flow rate of exhaust gas. A compressor wheel within a compressor component of the turbocharger is mechanically coupled to the turbine wheel, and is therefore rotatably driven by the turbine wheel. An inlet of the compressor receives fresh ambient air, and an outlet of the compressor is fluidly coupled to the intake manifold of the engine via an intake conduit. The rotatably driven action of the compressor wheel increases the amount of intake air supplied to the intake conduit, thereby resulting in an increased, or so-called “boost”, pressure therein.
With the development of increasingly sophisticated turbocharger and related automotive components, a need has arisen for extremely small package designs for turbocharger speed sensors utilized, for example, in diesel and gasoline engines. Current turbocharger speed sensors are used chiefly in laboratory settings or in a very limited basis at the center of a turbocharger housing. Locating the speed sensor instead on the compressor housing of the turbocharger takes advantage of cooler temperatures for sensor operations. The compressor housing location means that the sensor detects the speed of the compressor wheel as it spins at high RPM in the turbocharger. Such an arrangement also means that a hole or sensor bore through the compressor housing is required for the sensor face to be in close proximity to the fins of the compressor wheel.
Because the compressor wheel and compressor housing have been machined to close precision and the compressor wheel has been properly balanced, the added sensor bore and sensor must provide for a minimal operational impact. To prevent as little disruption as possible to the compressor wheel spinning at high RPM and to the airflow in the compressor housing, the speed sensor package should be configured in as compact and small an arrangement as possible. A small speed sensor package is also desirable for mounting or installation of the sensor on smaller sized turbochargers.
The cooler temperatures of approximately 190° C. on the compressor side of the turbocharger allow all of the integrated circuits (IC's) and signal conditioning electronics to be packaged together and over-molded with a thermoset and then the thermoset subassembly overmolded with a thermoplastic into a single package with an integral connector. Such a configuration eliminates the need for a pigtail or wire harness version of the sensor to remotely locate associated electrical components. A single integrated package can therefore reduce the number of components needed along with the associated material costs and manufacturing processes that would otherwise be required in a pigtail version. An integral connector version can thus allow for an enhanced sealing capability by eliminating multiple interconnects that would be necessary in a pigtail version.
In prior art sensor packages, the sense die is typically encapsulated in a thermoset package with external leads. The resulting IC package is then placed on a substrate such as a PCB or ceramic, along with other electronics. The substrate is then attached to a plastic carrier of some sort, encapsulated with thermoset for protection and then over-molded again with a thermoplastic to provide the final sensor package with integral connectors. A need exists for a sensor package and apparatus, which would allow for a much smaller sensor package than that afforded by conventional sensor packaging techniques and devices. It is believed that the sensor packaging methodology and devices described herein address this continuing need.